NORTON SHORES, Mich. – Several friends and acquaintances of a petite 25-year-old gas station clerk who went missing while working the night shift have been ruled out in her disappearance, which western Michigan investigators are treating as an abduction, the local police chief said Monday.

Police have frustratingly little evidence as they search for Jessica Heeringa, who disappeared Friday night shortly before the young mother was set to close an Exxon Mobil gas station in Norton Shores. The station didn't have a security camera and there were no signs of a struggle or robbery, though police have released a description of a vehicle and a man seen in the area.

Norton Shores Police Chief Daniel Shaw said relatives, friends and other people associated with Heeringa have been interviewed, and that investigators are "no longer really concerned with their activities from that night."

"We're moving on, trying to find other people," Shaw said.

Customers called police after finding the gas station open but no employees around. Investigators later found Herringa's purse and other personal belongings in the station, and the cash register untouched. Police described Herringa as 5-foot-1 and about 110 pounds.

"There's no sign of a struggle, no sign of anything inside the store being disturbed," Shaw said. "The cash drawer was sitting out and no money was missing. Her purse was in the store with 400-some dollars in it. It's just odd how that occurred."

Shaw said nearly two dozen law enforcement officials are following leads. The police chief described the city, home to about 24,000 people on the shores of Lake Michigan, as "quite safe" with a low rate of violent crime.

"The family believes that Jessica more than likely left to help (someone) in some way," Shaw said. "Their belief is that someone that she's either acquainted with or someone she was trying to help lured her out."

Police are searching for a gray minivan and its driver, who is described as a white man, age 30 to 40, about 6 feet tall, with light brown wavy hair. The description is from witnesses who saw the van parked near the station and driving away.

Heeringa's mother, Shelly Heeringa, told local media that she repeatedly told her daughter she worried about her working late by herself.